Problem faced while doing re-topology - can't maintain quads
Quick Aside: I find it easier to work from general to detailed when doing retopo work, doing the details and then trying to stitch them together means you lose control over the general topology flow because you are trying to reconcile your dense detail loops.

One of the first things you learn doing subdivision surface modeling is that you will need to cheat occasionally.  You will have to break one of your tenants every now and then, and knowing when and where is one of the primary ways to grow as an artist.  So, some suggestions:  


(Addition) One of the things LukeD was trying to point out with his comment and that I missed is that you want your mouth to be the radial anchor for the rest of the face.  This means that the concentric topology loops should be drawn from the mouth.  This allows for the least amount of unnatural deformation when posing the mouth and lips.  
If you want to preserve your flow, you should just extend the poly rows to the rest of the lip and have them converge at the lip's taper.  You would also keep your polys as quads, but they will be very small.  This is generally how it is done, see Polycount's face topology examples .
From experience, I would at least consider breaking the flow near there to deform in a collapsable way.  
You could also entertain putting a loop reduction quad there as well.
(edit) This is an arrangement of polygons that reduce loops in a way that allow high detail to low detail transitions, and look like such:   Source of picture and a great guide to using them effectively here:  http://topologyguides.com/post/163679954765/loop-reduction